Happy Eyeballs

happy_eyeballs.rb

require 'thread'

class ThreadInterrupt < RuntimeError; end

def try_ip
  if rand(2).zero?
    sleep 0.5
    true
  else
    sleep(rand(5) + 1)
    false
  end
end

def cleanup
  :noop
end

def eyeball(ip_list)
  success = false
  threads = []
  ip_list.each.with_index { |ip, idx|
    if !success # skip future ips if we've succeeded
      # wait 1 second before trying the next IP
      sleep 1 if idx > 0

      if !success # skip creating a thread if we've succeeded
        puts "trying #{ip}"
        threads << Thread.new {
          Thread.handle_interrupt(ThreadInterrupt => :never) {
            puts "in a thread"
            if !success # skip trying an ip if we've succeeded
              begin
                Thread.handle_interrupt(ThreadInterrupt => :immediate) {
                  success = ip if try_ip
                  puts "success: #{success}"
                }
              rescue ThreadInterrupt
                puts "received ThreadInterrupt"
              ensure
                Thread.handle_interrupt(ThreadInterrupt => :never) { cleanup }
              end
            end
          }
        }
      end
    end
  }
  if success # skip waiting for threads to finish
    threads.each { |t| t.raise(ThreadInterrupt) }
  end
  threads.each(&:join)
  success
end

eyeball [1, 10, 100, 100]